For cutting machining of a hardened steel or a heat resistant alloy, a sintered cubic boron nitride tool has been frequently used. For example, when a machine part such as a shaft of an automobile, etc., is to be produced by subjecting a hardened steel to cutting machining, a carburized layer existing at the surface of the hardened steel is removed by cutting machining, but depending on a shape of the material to be cut, a part which has not subjected to quenching is sometimes subjected to cutting machining. In such a high-load cutting machining, a temperature of the blade edge became extremely high, so that a sintered cubic boron nitride tool has been used in many cases. As a prior art technique of the sintered cubic boron nitride tool, there is a polycrystalline hard sintered body cutting tool in which a radius of curvature at a blade edge line portion is 5 μm or more and 30 μm or less, and a tool relief surface, and a tool rake surface or a negative land surface are smoothly connected to the above-mentioned radius of curvature.
See Patent Document JP 2001-212703A.